This application is based on Japanese Patent Application No. 2001-96525 filed on Mar. 29, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for controlling a valve timing, which controls at least one of valve timings of an intake valve and an exhaust valve of an internal combustion engine.
2. Description of Related Art
An apparatus for controlling a valve timing of an internal combustion engine is known in the art. The apparatus has a driving member rotating with a crankshaft (driving shaft) of the engine and a driven member rotating with a camshaft (driven shaft). The apparatus changes valve timing by rotating the driven member relative to the driving member using pressurized oil or the like. The apparatus controls the valve timing so as to improve an output of the engine or a fuel economy.
Hereinafter, the case of controlling an intake valve is explained. It is well known that closing the intake valve after the bottom dead center is effective to reduce the pumping loss of the intake air and to improve fuel economy. This valve timing is effective after the engine is warmed up. However, in a cold condition of the engine, this valve timing decreases an actual compression ratio and decreases a temperature of a compressed air at the top dead center. Therefore, this valve timing makes it difficult to start the engine.
It is also known in the art that the valve timing control apparatus can lock the valve timing at a position between a most advanced position and a most retarded position when starting the engine.
To locate the driven member in a starting position which is appropriate for starting the engine when the engine is started, it is desirable that the driven member is previously operated to the starting position or a position more advanced when the engine is stopped.
However, an engine speed is an idling speed or below when the engine is stopped. Therefore, it is difficult to supply a sufficient oil to operate the driven member. Moreover, in case of high oil temperature, it is more difficult to supply a sufficient amount and pressure of oil.
Meanwhile, it is desirable that an overlap period of the intake valve and the exhaust valve is relatively long to obtain stable combustions during an idling. Further, relatively retarded valve timing is desirable during the idling to reduce an improper combustion such as a knocking caused by a quick operation of an accelerator. Therefore, the starting position or more advanced position is undesirable in the idling.
An object of the present invention is to provide an improved apparatus for controlling a valve timing of an internal combustion engine.
Another object of the present invention is to provide an apparatus for controlling a valve timing, which can easily obtain a starting position that is appropriate for starting the engine.
A further object of the present invention is to provide an apparatus for controlling a valve timing, which can easily obtain the starting position even when oil is at a high temperature.
A still another object of the present invention is to provide an apparatus for controlling a valve timing, which can easily obtain the starting position with maintaining stable combustions during an idling.
According to a first aspect of the present invention, an apparatus for controlling a valve timing of an engine has a means for preparing an advancing control of the advancing means before the engine is stopped, the means controlling the engine into a condition that helps to advance the valve timing by the advancing means. The preparing means provides an advantageous condition that is effective to advance the valve timing when the engine is stopped. Therefore, if the operator operates the engine to stop, the engine is already in the condition preparing to advance the valve timing. As a result, the apparatus easily obtains an advanced valve timing that is close to the starting position when the engine is stopped.
According to another aspect of the present invention, an assist spring or a control means for a hydraulic actuator may be used for advancing the valve timing when the engine is stopped. The assist spring assists the camshaft to rotate in the advance direction. The control means controls the hydraulic actuator to rotate the camshaft in the advance direction.
According to a still another aspect of the present invention, advancing the valve timing may be helped by increasing an engine speed, advancing the valve timing previously, or decreasing a temperature of an oil supplied to the hydraulic actuator. For example, these preparations may be executed when the engine is in an idling since the engine is usually stopped from the idling.
According to a further aspect of the present invention, the valve timing may be advanced previously till combustion of the engine becomes unstable. Therefore, the combustion is kept in stable condition even if the valve timing is advanced during the engine is in the idling.
According to a still further aspect of the present invention, the variable valve timing actuator may include a lock mechanism which mechanically locks the camshaft and the crankshaft in the middle position.